1. Field of the Invention
This invention relates to a method for forming tires and more particularly, to an improvement in forming tires wherein a specific type of anti-sticking agent is applied to a drum bladder and a turnup bladder (hereinafter sometimes referred to generically as bladders) of a tire-forming machine, thereby preventing an unvulcanized rubber for tires from sticking to the bladders.
2. Description of the Prior Art
In preventing an unvulcanized rubber for tires from sticking to vulcanized rubber-made bladders of a tire-forming machine, it is the common practice to apply thereto solid or liquid release agents such as zinc stearate, paraffin wax and surface active agents. However, these agents undesirably need reapplication thereof every cycle of the tire forming or after several forming cycles. In addition, these agents have another disadvantage that when deposited on the unvulcanized rubber for tire, they will lower the quality of the resulting final tire depending on the type and amount thereof.
In order to solve the above problems, Japanese Laid-open Utility Model Application No. 51-150270 discloses a method in which a silicone rubber layer is formed on the surface of each bladder to give bladders of good release durability. Although this method is effective in improving the durability of release of the bladders from unvulcanized rubber, the bladders made of vulcanized rubber may be readily broken due to separation of the thus formed silicone rubber layer therefrom. This is because no technique is known for achieving a satisfactory bond between the bladders made of vulcanized rubber and the silicone rubber layer. Thus, practically adequate durability cannot be obtained. In order to overcome the ready breakage of such bladders, Japanese Laid-open Utility Model Application No. 56-41629 proposes a method using bladders made wholly of silicone rubber. Because of the substantial lack of physical strength of silicone rubber, however, the bladders so proposed have yet the disadvantage of being readily broken.
In view of the above, there have never been known any techniques of effectively preventing the sticking of unvulcanized rubber for tires to bladders made of vulcanized rubber, which sticking is invariably involved in methods of forming tires using tire-forming machines.